1. Field of the Invention
The present invention relates to a receiving apparatus.
2. Description of the Related Art
In radio communication, a received signal is subjected to filtering processing, frequency conversion processing, amplification processing and the like, to be demodulated to a baseband signal in general. Also, a receiving apparatus is generally known, which detects a reception status such as electric field intensity of the received signal or presence/absence of an undesired signal and which controls characteristics such as the filtering processing and the amplification processing according to the reception status, in order to improve communication quality in the radio communication.
For example, in FIG. 2 of Japanese Patent Laid-Open Publication No. 2003-174373, there is disclosed an adjacent interference detection unit for detecting an adjacent undesired signal using a first-method adjacent interference detection unit by a broad-narrow band difference method and a second-method adjacent interference detection unit by an adjacent band addition method. Also, in FIG. 14 of Japanese Patent Laid-Open Publication No. 2003-174373, there is disclosed an adjacent interference detection unit that can prevent wrong determination when a modulation degree of a desired signal is high by further using a third-method adjacent interference detection unit by an adjacent band difference method. Moreover, in Japanese Patent Laid-Open Publication No. 2003-174373, there is disclosed a broadcasting receiving apparatus for controlling the characteristics of the filtering processing and stereo separation (degree of separation) in a stereo demodulation unit according to a detection result in the adjacent interference detection unit.
As such, by using BPFs (Band-Pass Filter) having different passbands in combination, an adjacent undesired signal can be detected and communication quality of the receiving apparatus and sound quality of the broadcasting receiving apparatus can be improved.
However, since the third-method adjacent interference detection unit employed in the adjacent interference detection unit in FIG. 14 of Japanese Patent Laid-Open Publication No. 2003-174373 calculates a difference in amplitude level between an adjacent band higher than a frequency of the desired signal and an adjacent band lower than that, a smoothing processing unit having a sufficiently large time constant with respect to a frequency of the baseband signal is required. Thus, a response speed of the entire adjacent interference detection unit is limited by the time constant, and longer time is required for determining presence or absence of the adjacent undesired signal.